1. Field of the Invention
The present invention generally relates to polishing and planarizing work pieces. More particularly, the present invention relates to a method and apparatus for implementing replacement of polishing pads used for polishing and planarizing work pieces.
2. Discussion of the Related Art
Chemical mechanical polishing (CMP) is a well known planarizing method. CMP includes attaching one side of the wafer to be polished to a flat surface of a work piece carrier or chuck and pressing the other side of the work piece against a flat polishing pad. Polishing pads can be made of various materials which are commercially available. Typically, a polishing pad is made of blown polyurethane. The hardness and density of a polishing pad depends on the material that is to be polished. In CMP, a slurry containing a particulate abrasive such as cerium oxide, aluminum oxide, or fumed/precipitated silica is applied to a horizontal polishing pad during polishing to enhance the polishing process.
During polishing or planarization, the work piece is typically pressed against the polishing pad surface as the pad and/or the work piece rotates. In addition, to improve polishing, the wafer or pad can also be oscillated back and forth during polishing. It is well-known that polishing pads tend to wear unevenly during polishing, causing surface irregularities to develop on the pad and on the work piece. To ensure consistent and accurate planarization and polishing of all work pieces, such irregularities should be removed.
Furthermore, polishing pads used in CMP must be replaced periodically to ensure efficient polishing. As shown in FIG. 1, a typical CMP machine includes a polishing pad (10) attached, via adhesive (15), to a rotatable platen (25) positioned on a drive assembly that is disposed within a processing chamber of the CMP machine. During the replacement of such a polishing pad, a technician reaches into the processing chamber, grasps a portion of the polishing pad, and then pulls the polishing pad from the rotatable platen. The used polishing pad is then discarded. The remaining adhesive which fixed the polishing pad to the rotatable platen is then removed. Fresh adhesive is then applied in order to fix a new polishing pad to the rotatable platen.
Since the rotatable platen is typically two to three feet in diameter, it is difficult for a technician to replace a polishing pad while the polishing pad and rotatable platen are within the processing chamber. Accordingly, devices and apparatus for assisting removal and replacement of polishing pads have been conceived. For example, U.S. Pat. No. 5,551,136, issued to Bartlett, can be understood to teach a tool for removing a polishing pad from a rotatable platen. That tool includes a base, a lever member, at least one canted or angled latch pin, a chain having a plurality of links or rings, means for clamping the pad, and stop pins.
U.S. Pat. No. 6,221,199, issued to Chang et al., suggests a tool for removing an adhesively bonded pad from a backing plate. That tool includes a T-shaped removal tool that is rotated such that the adhesive bond between a pad and a backing surface is broken by a shearing force.
Additionally, U.S. Pat. No. 6,244,941, issued to Bowman et al., is understood to disclose a method for removing and replacing polishing pads utilized in CMP. The CMP polishing machine includes a rotatable platen with a top plate member having a top surface and means for removably mounting the top plate member to a top surface of the rotatable platen. The means for removably mounting the top plate member to the top surface of the rotatable platen uses electromagnets embedded within the top surface of the rotatable platen. The top plate member holds the polishing pad, which includes a magnetic material. Accordingly, activating the electromagnets attracts the top plate member to the top surface of the rotatable platen, thereby securing the top plate member against the rotatable platen. Additionally, the electromagnets are beneficially embedded within top surface of rotatable platen.
Finally, U.S. Pat. No. 6,033,293, issued to Crevasse et al., is understood to teach a polishing apparatus that includes a rotatable platen which is made of an upper plate and a lower plate. The upper plate is perforated with vacuum holes which open to a top surface. The lower plate contains vacuum channels that are coupled to the holes in the upper plate. A polishing pad includes an upper layer and a lower layer, wherein the upper layer is made of a material for polishing, while the lower layer is made of a hard material. In operation, the lower layer of the pad is placed in contact with the upper plate of the rotatable platen. A vacuum is created within the vacuum holes and vacuum channels, thereby securing the pad to the rotatable platen.
Although the previously described methods and apparatus for replacing a polishing pad are designed to facilitate replacing a polishing pad, they each require the introduction of a second device having multiple moving parts and/or introduces additional elements and features which may become worn and/or require maintenance. The introduction of such a second apparatus or device in facilitating the replacement of a polishing pad significantly increases the cost of the CMP process as well as the downtime for the CMP equipment. The introduction and installation of complex electromagnets embedded within the rotatable platen significantly increases the cost of the CMP equipment and may protrude from the top surface of the rotatable platen, thereby yielding an inconsistent surface for positioning a top plate member thereon. Furthermore, the introduction of specialized bi-layer pads increases the cost of the CMP apparatus.
Accordingly, there is a need for a simple method and apparatus which facilities the removal and replacement of a CMP polishing pad, so as to decrease down time and increase throughput without significantly increasing the cost, wear, and maintenance of the CMP machine.
It is therefore a principal object of the present invention to provide a method and apparatus for implementing the removal and replacement of a polishing pad during CMP processing.
It is still another object of the present invention to provide a method and apparatus for removing and replacing a polishing pad utilized in CMP processes which does not involve a significant increase in movable parts, specialized components, cost, and/or functional elements.
In brief, an apparatus according to the principles of the present invention includes a rotatable platen, a rigid plate member with a top surface and a bottom surface, and a vacuum channel that enables removably mounting the rigid plate member to a top surface of the rotatable platen. The vacuum channel is beneficially formed within the rotatable platen and includes a cavity in the top surface of the rotatable platen. The rigid plate member adhesively holds the polishing pad to form a rigid plate assembly. A vacuum source coupled to the vacuum channel can be activated to create a vacuum within the vacuum channel to attract the rigid plate member to the top surface of the rotatable platen. The rotatable platen can then used to polish work pieces contacting the polishing pad on the top surface of the rigid plate member.
In addition, an apparatus according to the principles of the present invention includes pin members coupled to the rigid plate member and which can be inserted into guide openings positioned within the rotatable platen.
The objectives, features and advantages of the present invention will become more apparent to those skilled in the art from the following more detailed description of the invention made in conjunction with the accompanying figures.